Polymer resin/inorganic filler-based composites are widely used as dental restorative materials and dental adhesives. In the US alone billions of dollars are spent in dental filling procedures using such materials every year. However, bacterial adhesion and biofilm-formation on such materials can lead to secondary caries, one of the major causes of the short service life (around several years) of the current resin-based dental restorations.
Three general methods have been tried to introduce antimicrobial functions into dental composites to control microbial adhesion and biofilm formation. The first method is to add monomeric organic antimicrobial agents directly into the composites. However, release of the antimicrobial agents will shorten the antimicrobial duration and deteriorate physical properties of the resulting materials. The second method is to add inorganic nano particles (e.g., silver, titanium dioxide, zinc oxide, etc.) into dental composites. However, the cost to prepare and use the nano particles is high, the complete mixing of the nano particles with the current dental composite formulation is difficult to achieve (e.g., nano particle aggregation occurs), and the potential health risk associated with the processing and use of nano particles is a concern. The third method is to add quaternary ammonium-containing monomers into the formulation to copolymerize with resin monomers. However, the new monomers have misciblity/compatiblity issues with the current resin monomers. In addition, quaternary ammonium salts have weak antimicrobial effects, and the effects can be quenched (stopped) by ionic compounds such as surface-active agents found in normal toothpastes.
In summary, antimicrobial activity is needed in resin-based dental restorative and adhesive materials that can inhibit microbial adhesion and secondary caries so as to prolong the service life of the resins. However, none of the current materials and methods provide a solution to these problems.